Head to head comparison of ${}^{68}$Ga-DOTA-FAPI-04 vs ${}^{18}$F-FDG PET/CT in the evaluation of primary extrapulmonary tumors in the chest

We conducted a prospective study using ${}^{18}$F-flurodeoxyglucose (${}^{18}$F-FDG) and ${}^{68}$Ga-DOTA-FAPI-04 (fibroblast-activation protein inhibitor, ${}^{68}$Ga-FAPI) PET/CT to diagnose, differentiate, and stage primary extrapulmonary tumors of the thorax. Fifty-four participants were undergoing ${}^{18}$F-FDG and ${}^{68}$Ga-FAPI PET/CT and divided into the benign, intermediate, and malignant based on pathology. The maximum standardized uptake value (SUVmax), the tumor-to-blood pool ratio, and tumor-to-liver ratio were compared for primary tumors, lymph nodes, and metastases between the two modalities by two independent samples t tests. One-way ANOVA was used to compare the uptake of ${}^{18}$F-FDG or ${}^{68}$Ga-FAPI among the three groups. Fifty-four participants were confirmed to have 71 primary lesions, 56 metastatic lymph nodes, and 43 metastatic lesions. ${}^{18}$F-FDG PET/CT could both effectively distinguish malignant lesions from non-malignant lesions, accuracies of 87.32% (p < 0.001).${}^{68}$Ga-FAPI PET/CT effectively differentiated benign lesions from the non-benign, accuracy being 91.55% (p < 0.001). The accuracies of ${}^{18}$F-FDG and ${}^{68}$Ga-FAPI for detecting lymph node metastasis were 77.22% (61/79) and 87.34% (69/79) (p = 0.096). The uptake of ${}^{68}$Ga-FAPI in metastatic lymph nodes was significantly higher than that of the nonmetastatic (p < 0.001). The detection rate of ${}^{68}$Ga-FAPI PET/CT for metastatic lesions was significantly higher than that of ${}^{18}$F-FDG, 100% (43/43) vs. 53.49% (23/43) (p < 0.001). Compared with ${}^{18}$F-FDG PET/CT, ${}^{68}$Ga-FAPI PET/CT changed the treatment strategy of 7.4% (4/54) participants. ${}^{68}$Ga-FAPI PET/CT is valuable in the diagnosis and differentiation of primary extrapulmonary tumors and superior to ${}^{18}$F-FDG PET/CT for evaluating lymph node and distant metastasis. The application of ${}^{68}$Ga-FAPI PET/CT in primary extrapulmonary chest tumors is valuable, which is reflected in diagnosis, differentiation and exploration of lymph node metastasis and distant metastasis.